add install librsvg to travis

.travis.yml

@@ -1,17 +1,26 @@
 language: node_js
+env:
+  - CXX=g++-4.8
 sudo: false
 node_js:
-- '0.10'
-- '0.12'
-- '4.0'
+  - '0.10'
+  - '0.12'
+  - '4.0'
 before_install:
-- npm install -g gulp
+  - npm install -g gulp
 install:
-- npm install
+  - npm install
 script:
-- gulp test
+  - gulp test
 after_success: cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js
   && rm -rf ./coverage
 notifications:
   slack:
     secure: a9AuzDgxCqlUF/eDEZuR1jbX8beIcdWKARvAvAh95eB3G/daWmo/A8SxOPCPW1VP34D/3lCrjF8HJZs3ItqAMuoLvWp3BFnmgTs8KkSIPVm9U7Q6Jcj9HhyCVPBUulprkf33Avj+eYIrUyaVTCZc8U4qaS8qZ5Djk1vCiJsBSk0=
+addons:
+  apt:
+    sources:
+    - ubuntu-toolchain-r-test
+    packages:
+    - gcc-4.8
+    - g++-4.8